The present invention generally relates to the field of polishing. In particular, the present invention is directed to a chemical mechanical polishing (CMP) pad having a radially alternating groove segment configuration.
In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting and dielectric materials are deposited onto and etched from a semiconductor wafer. Thin layers of conducting, semiconducting and dielectric materials may be deposited by a number of deposition techniques. Common deposition techniques in modern wafer processing include physical vapor deposition (PVD) (also known as sputtering), chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD) and electrochemical plating. Common etching techniques include wet and dry isotropic and anisotropic etching, among others.
As layers of materials are sequentially deposited and etched, the surface of the wafer becomes non-planar. Because subsequent semiconductor processing (e.g., photolithography) requires the wafer to have a flat surface, the wafer needs to be periodically planarized. Planarization is useful for removing undesired surface topography as well as surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches and contaminated layers or materials.
Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize semiconductor wafers and other workpieces. In conventional CMP using a dual-axis rotary polisher, a wafer carrier, or polishing head, is mounted on a carrier assembly. The polishing head holds the wafer and positions it in contact with a polishing layer of a polishing pad within the polisher. The polishing pad has a diameter greater than twice the diameter of the wafer being planarized. During polishing, the polishing pad and wafer are rotated about their respective concentric centers while the wafer is engaged with the polishing layer. The rotational axis of the wafer is offset relative to the rotational axis of the polishing pad by a distance greater than the radius of the wafer such that the rotation of the pad sweeps out an annular “wafer track” on the polishing layer of the pad. When the only movement of the wafer is rotational, the width of the wafer track is equal to the diameter of the wafer. However, in some dual-axis polishers, the wafer is oscillated in a plane perpendicular to its axis of rotation. In this case, the width of the wafer track is wider than the diameter of the wafer by an amount that accounts for the displacement due to the oscillation. The carrier assembly provides a controllable pressure between the wafer and polishing pad. During polishing, a slurry, or other polishing medium, is flowed onto the polishing pad and into the gap between the wafer and polishing layer. The wafer surface is polished and made planar by chemical and mechanical action of the polishing layer and polishing medium on the surface.
The interaction among polishing layers, polishing media and wafer surfaces during CMP is being increasingly studied in an effort to optimize polishing pad designs. Most of the polishing pad developments over the years have been empirical in nature. Much of the design of polishing surfaces, or layers, has focused on providing these layers with various patterns of voids and arrangements of grooves that are claimed to enhance slurry utilization and polishing uniformity. Over the years, quite a few different groove and void patterns and arrangements have been implemented. Prior art groove patterns include radial, concentric circular, Cartesian grid and spiral, among others. Prior art groove configurations include configurations wherein the width and depth of all the grooves are uniform among all grooves and configurations wherein the width or depth of the grooves varies from one groove to another.
Some designers of rotational CMP pads have designed pads having groove configurations that include two or more groove configurations that change from one configuration to another based on one or more radial distances from the center of the pad. These pads are touted as providing superior performance in terms of polishing uniformity and slurry utilization, among other things. For example, in U.S. Pat. No. 6,520,847 to Osterheld et al., Osterheld et al. disclose several pads having three concentric ring-shaped regions, each containing a configuration of grooves that is different from the configurations of the other two regions. The configurations vary in different ways in different embodiments. Ways in which the configurations vary include variations in number, cross-sectional area, spacing and type of grooves. In another example of prior art CMP pads described in Korean Patent Application Publication No. 1020020022198 to Kim et al., the Kim et al. pad includes a plurality of generally radial non-linear grooves that: (1) curve in the design rotational direction of the pad in a radially inward portion of the pad; (2) reverse curvature within the wafer track and (3) curve in the direction opposite the design rotational direction proximate the outer periphery of the pad. Kim et al. indicate that this groove configuration minimizes defects by rapidly exhausting byproducts of the polishing process.
Although pad designers have heretofore designed CMP pads that include two or more groove configurations that are different from one another or vary in different regions of the polishing layer, these designs do not directly consider benefits that may arise from varying the speed in which the polishing medium flows in the gap between the wafer and the pad across the width of the wafer track. Current research by the present inventor shows that polishing can be improved by permitting the polishing medium to flow relatively rapidly within the pad-wafer gap in one or more regions of the wafer track while inhibiting the flow of the polishing medium in one or more other regions of the wafer track. Consequently, there is a need for CMP polishing pad designs that control, and vary the speed of, the flow of polishing media within the pad-wafer gap.